Process for sensitizing silver halide emulsions



July 12, 1960 o. RIESTER 2,944,896

PROCESS FOR SENSITIZING SILVER HALIDE EMULSIONS Filed May 16. 1956 Sensihzohon with dye of Example L 'm/L 400 450 506 Sensifizor'on with dye of Exu mple 2 m/u, 400 450 500 39- 5. Sensitizationwith dye of Example 4 29 Sensitization with dye of Example 7 INVENTOR.

OSKAR R/E 5 TE R ATTORNEYS PRQCESSEORSENSITIZING SILVER EMULSIONS:

Oskar-Riester, Leverkusen, Germany, assignor to Agfa Aktiengesellschaft, a corporation: oii'Grermany Filed May 16, 19 56, Ser. No. 585,146 Claims priority, application Germany May 25, 1955 8 Claims. (Cl; 96-"-63) It is known that silver halide, emulsions show an inherent sensitivity in theviolet' zone-ofthe spectrum. Particularly with silver chloride emulsions, only a small part of the sensitivity is in the range of visible light, while the main sensitivity is in the ultra-violet. When used practically, however, the efiect of the glass intercalated between the light source and the emulsion layer is to cut off by far the greatest part of this sensitivity. The main effect of this is seen when the exposure is made with artificial light, because the short-Wavespetra-l zone. thereof is veryslight.- Therefore, with the photographic copying process, only a smalli'pa-rtof 1118 eifectivelight is utilized.

It is known that anew sensitivity ran-gecan be added to thephotographic emulsion for visible light by introducing dyestuffs and-thus a better light yield,- i.e. a higher total sensitivity, isobtaineda Howeverya serious disadvantage.whichzisthereby pro; duced. is that only a smaller part of' the visible .li'ght,spec-, available-for the processing in fthQ; darkeroom. since it isv in. fact-necessary to exclude .thoserrays :for which the photographic layer has additionally been made sensitive. Consequently, for. {the ;-lighting in, the. ..dark-. room, it is necessary to use .a flight which. physiologically appears darker, but. this makes .-it, substantially more difiicult toyjudge the image appearing during development; .is: particularly undesirable when, the. image involved isapc itive mage. f rample-1a P89 ima e- Actually, these images are in practice best produced with the psysiologically very bright yellow light, for example, of the Agfa dark-room filter 1-12, with which it is possible to estimate very satisfactorily the condition of the image formed as regards the correct. gradation and density. It would of course be possible touse a pure silver chloride emulsion, Whichcan then 'be readily processed with bright yellow light. Insuch cases, howeveneomparatively long exposure times are obtained, especially with hard layers. If this silver chloride emulsion is sensitized, there is obtained an increase in the sensitivity and thus the desired reduction of the copying time. Simultaneously, however, the sensitivity to the yellow dark-room light is increased in an undesirablemanner,'so thatexposurestake place which have the effect of varying' the gradation or even of fogging.

It" has now been found that an increase in-the sensitivity of the silver halidei-emulsionss'can be; :.achieved without: deleteriously affecting. dark-room safetyg-if; :neut-rocyanines ofthe following general formula:

are used for sensitization-. v

In this formula: R stands-for alkylgsuchias methyl, ethyl, propyl, butyl, amyl, 'alkyl, dfldflQYl,.iSQPIOP1,.-i$0r butyl, isoamyl, cycloalkyl, such as cyclohexyl, ary-l such 2,944,896 HatentedsJuly; 12,1950.

ice

. 2' as. :phenyl; chlorphenyl, naphthyl, furyl, .aralkyl such as benzyl, phenyl'althyl, organic? radicals. which contain a free carboxylic acid groupysuch' as alkylenecarboxy-i groups as for instance group, organic. radicals'which: contain an. esterified acid groups such as -CH CO0H, CH CH COOH groups which are esterified with aliphatic and cycloaliphatic alcohols such as methyl-, ethyl, cyclohexylalcohol, organic radicals which contain asulfonic. acid group such as alkylensulfonic and groups as for instance propylene-w sulfonic acid, butylene-w sulfonic acid groups, and

R and R stand for alkyl, cycloalkyl, aralkyl, aryl or a heterocyclic radical without nitrogen, such as furyl or thienyL. any- -such:rad-ical..being. substituted in place :of anzappropriatenumber of hydrogen atoms. of the CH groups, the. left; handaring, .onralternatively the I left; hand ring may be :unsubstitutei R and R ,being-the same omdiif'erenhmhilerR, and R3 or R and R may be. joined to form. aring;

n=awholenumber fr'orni3, to 12;

.=atomic"groups necessary for: closing a five= andfsixmembered ring. Ring systems of this type are for ex-. ample:- thiohydantoin,; rhodanine, isorhodanine, selenorhodanine, .oxythionaphthane, indandione, pyrazolone (-5).

The entire dyestutf molecule can also be multiplied, forexample, bythe. ring nitrogen. atoms being combined with one another by a divalent organic radical, such as for example an alkylene group. Such dyestufis may be (H2 a Bi and.

Imtheseiormulae n, R R R and A have the same significance. as. in the; first. formula, whereasR stands for abivalentorganic radical such as an alkylene group.

'Ihese; neutrocyanines are producedlaccording. to the prQQess-ofiGennan Patent 927,043. i

Particularly withsuchlphotographic. emulsions as consist predominantly of silver chloride, the dyestuffs yield increases in sensitivity up to. 10. times the inherentrsensitivity and neverthelesspermit a perfect processing with bright. yello,w.light. Substantial advantage. of these sen'si. tisers consists in that completely uncoloured layers are left after the processing when they are used, whereas otherwise with good sensitisers, a so-called residual-colouring frequently remains in the gelatine or in the baryta layer, this being evident by a yellowish toning similar to a yellow fogging.

An additional advantage is their stability with respect to the conventional-emulsion additives, such as stabilisers, wetting agents, fluorescing substances, etc.

The sensitisers are added in amounts of for example 3 to mg. per litre. of emulsion, depending on the increase in sensitivity which is desired. It can be added at mega, Hyman)...

' 3 any desired time, for example, as a casting additive to the finished emulsion or already in the final digestion, or the sensitisers are used in the so-called bath process.

The effectiveness of these sensitizers is more clearly shown in the following examples and in the/accompany ing drawings where the individual figures show the efiect produced by some of these examples.

. Example 1 'The yellow dyestuff of the following constitution:

4} :0 H2 /0 ([3 O=S N Example 2 The pale yellow dyestuff, of the following constitution:

yields an increase of about 7 times in the sensitivity with a silver chloride emulsion of average contrast. Sensitization maximum is in the region of 434 me.

The dyestuff is prepared as follows: 7

2-piperidone is dissolved in chloroform and treated with excess phosphorpentasulfide at a temperature of 40. The resultant Z-thiopiperidone has the boiling point l84l85 at 13-14 mm. Hg. The thiopiperidone is re acted in an alcoholic sodium 'alcoholate solution With methyliodide to form 2-methyl-mercapto-3,4,4,6-tetrahydropyridine, which latter is a liquid of the boiling point 71-79 at 13 mm. Hg. 71.3 g. Z-methylmercaptotetrahydropyridine and 1 ml. of 'dimethylsulfate are heated with one another, the mixture substantially rises in temperature and reacts vigorously. It is heated to 90 .C. for a further 5 minutes, the reaction product is cooled, 2.1 g. N-ethylrhodanine and 60 cc. of absolute alcohol are added. Thereupon 2 cc. of triethylamine are added and the mixture is refluxed on the water bath for 30 minutes. The dyestufi crystallizes out while boiling. It is recrystallized from a solution of pyridine and alcohol.

Example 3 The dyestufi of the following constitution: v

s H2 I) l N e a yields an increase by about 5 to 6 times and the sensitization maximum is in the region of 442 mp.

The dyestufi is prepared as follows:

3.2 g. of N-phenyl-Z-thiopyrrolidone-metbiodide (which is obtainable from N-phenyl-Z-pyrrolidone by melting with excess phosphorus pentasulfide at 130 C. and reacting the thus obtained thiopyrrolidone with methyliodide). and 1.6 g. N-ethylrhodanine are mixed and treated with 20 cc. of absolute alcohol and 2 cc. of triethylarnine. The mixture is refluxed on a Water bath for 30 minutes. The dyestufl re-crystallizes upon cooling. It is re-crystallized from 50 cc. of methanol.

Example 4 yields an increase of about 6 times in the initial sensitivity of a contrasty silver chloride emulsion with the addition of 30 mg. to 1 kg. of emulsion. The sensitization maximum is in the region of 434 m The dyestuff is prepared as follows:

T he thiolactam as obtained from caprolactam by sulfurization with p s is methylated with dimethyl-sulfate in diluted caustic soda solution and distilled in vacuum t ture'i's'heated on an oil bath for 5 minutes at 90 C.

The reaction mixture is cooledin ice water, 1.6 g. N-ethylrhodanine are added and treated with'20 cc. of absolute alcohol and 2 cc. of trieth-ylamine. The mixture is heated to boiling on the water bath for 30 minutes. The hot yellow dystutf solution is mixed with 20 cc. of Water, the mixture is cooled in ice water. A yellow, crystallized dyestuflf is obtained. It is dried in the exsiccatorov'er sulfuric acid and i e-crystallizes from methylisoheptane.

Example 5 The increase is sixfold. The sensitization maximum is in the region of 436 mu.

The dyestuft' is prepared as follows:

5-spirocyclohexyl-pyrrolidone-(2) is melted with excess phophorus pentasulfide at 130 C. Z-mercaptomethyl-S- spiorcyclohexyl-l-pyrroline is thus obtained. This substance is a liquid of the boiling point l27l28 at 19.5 mm. Hg. 1.8 g. of the thus obtained pyrroline and 1 cc. of dimethylsulfate are heated to for 10 minutes. The reaction mixture is cooled and 1.6 g. of N-ethylrhodanine, 20 cc. of absolute alcohol and 2 cc. of triethylamine are added. The mixture is refluxed to boiling for 30 minutes. The dyestufi becomes crystalline while boiling. It is cooled in ice water and filtered with suction. The dyestufi is re-crystallized for several times from 200 cc. of alcohol.

. l Example 6 1 The-increase 7 to 8 times. The sensitization maximum is in the region of 456 me.

The dyestufl is prepared as follows:

3-cyclohexyl-pyrrolidone-(2) are converted, as described in the foregoing example, in 2-mercaptomethyl-3- cyclohexyl-l-pyrroline. The pyrroline is a liquid of the boiling point 151C. at 21 mm. Hg. 2 g. of pyrroline thus obtained and 1 cc. of dimethylsulfate are heated in the oil bath for 10 minutes to 100 C. The reaction mixture is cooled, 2,6 ggof N-phenyl-selenorhodanine 10 cc. bf piiridiiie'and 1.5 cc.oftriethylamine are added. The mixture is heated to 100 C. in the oil bath for 1 hour. It is then treated while hot with5 "cc. of alcohol and 20 cc. of water. Upon cooling for a long period the dyestuff becomes crystalline. The dyestufi is filtered with suction and re-crystallizedforseveral times from 50 cc. of alcohol.

olic solution ofthe dyestufl absorbs the ultraviolet specand added to a silver chloride emulsion prior to casing.

s solved 'metlillliwrlolidone 'in the ratio of 1 1 1 000 at 3 mm. Hg).

. 6 The increase in sensitivity is 6 to 7 times the sensitization maximum is in the region of 439 m The dyestufl: is prepared as follows:

5.6 g. of N,N-hexamethylene-bis-(thiopyrrolidone-2) and 5 cc. of dimethylsulfate are heated at 100 C. for 10 minutes. After cooling 8 .g. of N-ethylrhodanine in cc. of pyridine are added and the mixture is heated on the steam bath for 15 minutes. Upon addition of 150 ml. of ice water the dyestuff precipitates as a semisolid massand is re-crystallized after isolation from 250 of methanol-chloroform (1: 2.). The absorption of the inethanolic solution is in the ultraviolet spectrum.

The hexamethylene-bis-(pyrrolidone-Z) is prepared by heating 116 g. of hexamethylenediamine with 175 g. of butyrolactone in the autoclave at 260 280 C. for 3 h61irs andsubsequent distil1ation (B.P. 226-228 C. 100 g. of this pyrrolidone are stirred with 86fg.phosphorus pentasulfide in 350cc. of xylene .and 53g. of magnesia at 12044 0 for 30 minutes. Thereu on it isdecomposed with ca. 200 cc. of water and '100 'cc.,of sodium hydroxide. solution, the oil is separated, dried with potash and distilled The "N,N'- hexamethylene-bis-(thiopyrrolidone) distilled -over at 280295 under 2 miii. Hg.

Eicample 9 A dyestufi ofthe constitution:

CH. S Hill (i=0 H2 0 C=S N N H i H B 5 H2O /S\ 2 /C=C C: 0: N/ (52H:

dissolved in acetoneimethyl pyrrolidone (1:1) yields 7 an increase up to 9 times with a very contrasty silver chloridezemulsion; the sensitiiationmaximum is in the region 5442 my" The "dyestufi is prepared as follows:

, heated on the steam bath for 15 minutes, 2.8 cc. of tricthylamine are added and the mixture is reacted on the steam bath for a further 50 minutes. After precipitating with 150 cc.of ice-waterthe mixture is left standing on the ice for 2' hours and the precipitated crystals are then filtered; with suction. The crystals are recrystallized from chloroform. The methanolic solution absorbs in the ultraviolet region of the spectrum.

.xtainediby evaporating the-benzenic solution after standing for some time. M.P. 143 C.

.7 Example 10 A dyestufi of the constitution:

yields an increase in sensitivity up to 3 to 4 times in a silver chloride emulsion; the sensitization maximum is in the region of 430 m The dyestufr' is prepared as follows: a

4.4 cc. of N-methyl-thiopyrrolidone(2) and 4 cc. of dimethylsulfate are reacted by heating in the steam bath. After cooling 2 cc. of N-ethyl-oxazolidone-(2)thione- (5) in cc. of pyridine and thereafter l cc. of triethylamine are added. The mixture is left standing at 40 C. for 5 hours and the dyestuif formed -is precipitated with 200 cc. ice water. The dyestufE is filtered with suction and re-crystallized from methanol after. The solution in methanol absorbs the ultraviolet.

yields an increase by .9 times with a silver chloride dimethylsulfate are reacted by heating to about 90 C.

The mixture is slowly cooled and 2 g. of ethylenerhodanine in 20 cc. of pyridine are added and the mixture is heated to about 40 C. for 12 hours. The formed dye stufi is thereafter precipitated by addition of water and re-crystallized from methanol and chloroform (1:1). The methanolic solution absorbs the spectral violet and ultraviolet.

I claim:

1. An optically sensitized silver halide emulsion. layer in which at least 98% of the silver halide is' silver chloride, said emulsion containing as essentially the only optical sensitizer a neutrocyanine of one of the formulae selected from the group consisting of U r ,B V r I and III

in which R stands for a substituent selected frqm the C2115 3. The combination of claim 1 wherein the sensitizer is 5. The combination of claim 1 wherein the sensitizer is wherein the sensitizer V I CH2 H20 I r N V a I 7 6H CH.

7. A method formakingphotographic reproductions, said method including the steps of providing a support that carries the optically sensitized silverh'alide emulsion of claim 2; exposing .the emulsion to the desired optical 'image, and developing the; exposed emulsion in a developer for exposed silver halide and in a relatively bright yellow light. a

SifAn optically sensitized'isilvei halide emulsion layer 'in which atleast'98%. of the saver halide is silver chloride, said emulsion containing as essentially the only optical sensitizer a neutrocyanine having the formula V /B\\7 V LOT-= in which R stands for a substituent selected from the group consisting of alkyl, cycloalkyl, aralkyl, and aryl radicals; .A represents the non metallic atoms necessary to complete a n'ng selected from the group consisting of thiohydantoin, rhodanine, isorhodanine, selenorhodanine, oxythionaphthene, indandione, and pyrazolone-S rings; and B stands for a saturated bivalent aliphatic hydrocarbon radical having a chain length of 3 to 5 carbon 5 atoms completing the ring with the N-C chain.

References Cited in the file of this patent UNITED STATES PATENTS 2,166,736 White et a1 July 18, 1939 10 2,213,730 Beilenson Sept. 3, 1940 2,322,015 Hamer et a1 June 15, 1943 FOREIGN PATENTS 927,043 Germany Apr. 28, 1955 OTHER REFERENCES Mees: The Theory of the Photographic Process, re- 0 vised edition, page 4-13, MacMillan Co., New York. 

1. AN OPTICALLY SENSITIZED SILVER HALIDE EMULSION LAYER IN WHICH AT LEAST 98% OF THE SILVER HALIDE IS SILVER CHLORIDE, SAID EMULSION CONTAINING AS ESSENTIALLY THE ONLY OPTICAL SENSITIZER A NEUTROCYANINE OF ONE OF THE FORMULAE SELECTED FROM THE GROUP CONSISTING OF 